1. Field of the Invention
The present invention relates to a packet data transmission, and particularly, to a system and method for determining transmission power of packet data.
2. Background of the Related Art
A mobile communication system using radio packet data transmission at high speed is a system for providing communication service between mobile stations such as a potable terminal or a car phone, or between a mobile station and a telephone subscribed in a PSTN (Public Switched Telephone Network).
Generally, a radio communication network such as the mobile communication system uses a circuit method and a packet method in order to provide a data service.
The circuit method is a method which allocates needed resources and channels to a transmission node which will transmit data, and the allocated channel is a dedicated circuit for the duration of the call. By contrast, the packet method is a method excluding monopolies on the channel, where a channel is allocated to a corresponding transmission node only when there is data to be transmitted. In a packet method, the allocated channel is released when the data transmission is completed, and thereby the other transmission mode can transmit data.
FIG. 1 is a block diagram showing a related art mobile communication network including multiple mobile stations 10 and a base station 20.
FIG. 2 is a flow chart showing a related art circuit switched data transmission process. As shown, the data transmission process of a circuit method includes setting a call between a transmission node and a receive node (S1) and allocating resources such as time slot, a trunk, and a memory device after the call is set (S2). The process further includes transmitting data through the allocated resources and channel (S3) and releasing the allocated resources when the data transmission is completed (S4, S5).
In the data transmission system of a circuit method, a call should be set between the transmission node and the receiver node before the data is transmitted. In addition, resources such as the time slot, the trunk, and the memory device, which are needed for data transmission, are allocated by the system when the call is set.
When the call setting is completed and a channel is allocated, the corresponding call occupies the allocated channel until the data transmission is completed. When the data transmission is completed, the system releases the resources allocated for the data transmission.
As described above, the circuit method uses all bandwidth provided by the system, and a large amount of data can be transmitted. However, only about 5% of the connection time is used for the data transmission, and therefore the utility of the channel and the number of calls which can be accepted is small.
As described above, the circuit method is not suitable to provide high through-put communications, and therefore the packet method has been developed for IMT-2000 (International Mobile Telecommunications 2000) service.
FIG. 3 is a flow chart showing a related art packet switched data transmission process. As shown therein, the data transmission of a packet method includes identifying whether or not there is transmission data in the transmission node (S11) and allocating a channel if there is transmission data in the transmission node (S12). The method further includes transmitting the data after the channel is allocated (S13) and releasing the allocated channel when the data transmission is completed (S14, S15).
Data transmission by the packet method occupies the channel only when data is included in a respective transmission node, and therefore more transmission nodes can transmit data and the utility of the channel can be increased.
FIG. 4 is a signal diagram showing signals in the data transmission process of a packet method suggested by the 3GPP (3rd Generation Partnership Project) the asynchronous part of IMT-200, and FIG. 5 is a conceptual view according to that same method.
CPCH (Common Packet Channel) suggested by the 3GPP is a method in which a channel is set before data transmission and the data is transmitted when the channel is set, similar to the circuit method. It is different from the circuit method in that the channel is allocated only when there is data to be transmitted on the transmission node.
As shown in FIG. 4, the CPCH data transmission of the 3GPP method includes transmitting an AP (Access Preamble) from a mobile station 10 to a base station 20 (S21) and transmitting an AP-AICH (Access Preamble-Acquisition Indication Channel-acknowledge) signal from the base station 20 to the mobile station 10 as a response to the AP signal (S22). The method further includes transmitting a CD (Collision Detection) Preamble from the mobile station 10, which received the response, to the base station 20 (S23) and transmitting a CD-AICH (Collision Detection-Acquisition Indication Channel-acknowledge) signal from the base station 20 to the mobile station 10 as a response signal to the CD preamble signal (S24). Finally, the method includes transmitting information data and control data from the mobile station 10 to the base station 20 (S25).
Referring to both FIGS. 4 and 5, the mobile station 10 transmits an AP at position P0 with a lowest level of transmission power set by the system in step S21. If the base station 20 does not receive the AP transmitted from the mobile station 10 on position P0, the base station 20 can not be synchronized and can not generate a response signal AP-AICH. Therefore, the mobile station 10 again transmits the AP at position P1 after a prescribed period of time is passed, with a transmission power which is increased at a prescribed level greater than that of the AP transmitted from the position P0 in step S21.
When the base station 20 receives the AP, the base station 20 indicates that the signal is synchronized by transmitting an AP-AICH signal to the mobile station 10 as a response in step S22, and then the mobile station 10 transmits a CD-preamble to the base station 20 in step S23. In addition, the base station 20 transmits a CD-AICH signal to the mobile stations 10 as a response to the CD-preamble signal in step S24. The CD-preamble signal is for preventing impacts when more than one mobile station 10 requests allocation of the same channel at the same time.
The mobile station 10 prepares for the data transmission by passing through steps S21, S22, S23, and S24. The mobile station 10 then transmits information data and control data through a PCPCH(UL) (Physical Common Packet Channel(Up Link)) to the base station 20 in step S25. In addition, the base station 20 regularly transmits signals for power control, pilot, and CPCH control to the mobile station 10 through a DPCCH(DL) (Dedicated Physical Control Channel(Down Link)).
The method of the related art has many problems. For example, in the case of the packet method suggested by 3GPP, a plurality of AP's are transmitted for the respective packets, and the first AP is transmitted with the lowest level of transmission power set by the system for minimizing interruption to the other channels. Thus, accessing the base station takes a long time using this method, since the AP is transmitted with initial transmission power which has fixed level, and the accessing process is performed each time a packet is transmitted. The disadvantageous delays associated with initial transmission power adjusting times, t, are illustrated in FIG. 6. Accordingly, high speed data transmission is difficult.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.